Learn Hardcore Indonesian: Insinyur muda itu menulis artikel tentang jembatan baru di kota; penulis senior mengedit bahasanya. - That young engineer writes an article about the new bridge in the city; a senior writer edits the wording.

Itu is a demonstrative that usually means that, but in Indonesian it is also very commonly used like the to mark something as specific/known.

Insinyur muda itu can be translated as that young engineer or the young engineer, depending on context.
When itu comes after the noun phrase (insinyur muda
- itu), it usually marks a specific, known person/thing.

If you said only insinyur muda, it would sound more like a young engineer (non-specific).

Why is it Insinyur muda itu, not Itu insinyur muda?

These two patterns mean different things:

Insinyur muda itu
→ literally young engineer that = that young engineer / the young engineer
This is a noun phrase describing a specific person.
Itu insinyur muda
→ literally that (is a) young engineer
This is a full sentence, something like That is a young engineer (e.g. pointing at someone).

So in the example sentence, we need a subject noun phrase, not an equative sentence like That is a young engineer.

What is the general word order with adjectives like muda, baru, and senior?

In Indonesian, descriptive words (adjectives) usually come after the noun:

insinyur muda = young engineer
jembatan baru = new bridge
penulis senior = senior writer

So the basic pattern is:

Noun + Adjective

This is the opposite of English, where adjectives usually come before the noun (young engineer, new bridge, senior writer).

Does menulis specifically mean wrote, or can it also mean is writing / writes?

Menulis is not marked for tense. It simply means to write / writing.

The tense is understood from context or added time words:

Kemarin insinyur muda itu menulis artikel.
Yesterday that young engineer wrote an article.
Sekarang insinyur muda itu menulis artikel.
Now that young engineer is writing an article.
Setiap hari insinyur muda itu menulis artikel.
Every day that young engineer writes articles.

In your sentence, translating menulis as wrote is a natural English choice, but the Indonesian itself is tense-neutral.

What is the difference between menulis and tulis?

The base word is tulis (write).

Menulis = meN- + tulis

menulis is the standard active verb form = to write / writing / writes / wrote
tulis on its own appears in:
- commands: Tulis namamu! = Write your name!
- certain fixed expressions and noun forms (e.g. penulis = writer)

So in normal sentences with a subject, you use menulis:

Insinyur muda itu menulis artikel.
The young engineer wrote/is writing an article.

What does tentang mean in artikel tentang jembatan baru di kota?

Tentang is a preposition meaning about / concerning.

artikel tentang jembatan baru di kota
= an article about the new bridge in the city

Other words similar to tentang:

mengenai – also about / regarding (often a bit more formal)
perihal – quite formal, often in letters/documents

In everyday speech and writing, tentang is the most common and neutral choice for about.

What’s the difference between di kota and something like di sebuah kota or di kota itu?

di kota = in the city (city in a general or context-known sense)
di sebuah kota = in a city (non-specific, one city, we don’t care which)
di kota itu = in that city / in the city (already mentioned/specified)

In your sentence, di kota is vague on purpose: it could be in the city where they live/work, understood from context. If the city had been identified before, di kota itu would sound more precise.

What does penulis mean, and how is it related to menulis?

Penulis means writer/author.

It is formed from:

peN- (a prefix that often forms agent nouns)
- tulis (write)

So:

menulis = to write
penulis = writer (the person who writes)

Other examples of this pattern:

mengajar (to teach) → pengajar (teacher)
menyanyi (to sing) → penyanyi (singer)

What exactly does bahasanya mean in penulis senior mengedit bahasanya?

Bahasanya is bahasa + -nya.

bahasa = language, wording
-nya can mean his/her/its/their, or function like the in some contexts.

In this sentence, bahasanya means something like:

its language / its wording / the language (used in it)

So penulis senior mengedit bahasanya is not about changing the content, but polishing the language/wording/style of the article.

How is mengedit formed, and is it different from just edit?

The base word is the loanword edit (from English).

Mengedit = meN- + edit

mengedit is the normal active verb form: to edit / is editing / edited.

In casual speech, some people might just say edit in certain constructions (e.g. boleh saya edit?), but in standard Indonesian, with a clear subject, mengedit is preferred:

Penulis senior mengedit bahasanya.
The senior writer edited its language/wording.

Is the semicolon ( ; ) used in Indonesian the same way as in English here?

Yes, broadly similar.

In this sentence, the semicolon:

connects two closely related clauses:
Insinyur muda itu menulis artikel tentang jembatan baru di kota; penulis senior mengedit bahasanya.
shows that the second clause is directly related to the first (someone else edits what was written).

You could also split it into two sentences with a period:

Insinyur muda itu menulis artikel tentang jembatan baru di kota. Penulis senior mengedit bahasanya.

Both are correct; the semicolon just ties them more tightly together.